1. Field of the Invention
The present invention relates to a magnetic detecting device including a first and a second magnetoresistive element having opposite interlayer coupling magnetic fields +Hin and −Hin and to a method for manufacturing the same, and particularly to a magnetic detecting device whose magnetoresistive elements have a small difference in temperature coefficient of resistance (TCR) and are connected in series to respective fixed resistors formed in the same process.
2. Description of the Related Art
Giant magnetoresistive elements (GMR elements) using the magnetoresistive effect are used in magnetic sensors (magnetic detecting devices).
For example, a magnetic sensor disclosed in Japanese Unexamined Patent Application Publication No. 2006-253562 (FIG. 12) includes four resistors constituting a bridge circuit. Two of the four resistors are magnetoresistive elements, and the other two are fixed resistors having constant electric resistances independent of the external magnetic field.
When an external magnetic field oriented in a direction is defined as a (+)-direction external magnetic field and an external magnetic field oriented in the opposite direction to the (+) direction is defined as a (−)-direction external magnetic field, the magnetic sensor can be of bidirectional type configured to detect both the (+)-direction external magnetic field and the (−)-direction external magnetic field. In this instance, the magnetic sensor is configured so that a first interlayer coupling magnetic field Hin 1 acting between the pinned magnetic layer and the free magnetic layer of one magnetoresistive element (hereinafter referred to as first magnetoresistive element) can be positive, and so that a second interlayer coupling magnetic field Hin 2 acting between the pinned magnetic layer and the free magnetic layer of the other magnetoresistive element (hereinafter referred to as second magnetoresistive element) can be negative. Thus, the resistance of the first magnetoresistive element can be varied by the (+)-direction external magnetic field and the resistance of the second magnetoresistive element can be varied by the (−)-direction external magnetic field.
Thus, a bidirectional magnetic sensor can be achieved by using two magnetoresistive elements having opposite interlayer coupling magnetic fields +Hin and −Hin.
Japanese Unexamined Patent Application Publication Nos. 2006-266777 and 2006-208255 also disclose such magnetic sensors.
In order to give opposite interlayer coupling magnetic fields +Hin and −Hin to the first and second magnetoresistive elements, the antiferromagnetic layers of the magnetoresistive elements may have different thicknesses from each other, or the magnetoresistive elements may be formed of different materials or have different multilayer structures.
However, those modifications of the magnetoresistive elements increase the difference in TRC between the first and the second magnetoresistive element.
In order to adjust the TCRs of the fixed resistor (first fixed resistor) connected to the first magnetoresistive element in series and the fixed resistor (second fixed resistor) connected to the second magnetoresistive element to the TCRs of the respective magnetoresistive elements, the first and second fixed resistors must be formed of different materials or in different layer structures in different process steps.
Accordingly, in the known manufacturing process, the first magnetoresistive element, the second magnetoresistive element, the first fixed resistor, and the second fixed resistor must be formed in different process steps. The known manufacturing process is thus complicated.
In addition, if the magnetoresistive element and the fixed resistor connected to the magnetoresistive element in series have different TCRs, the midpoint potential may be varied with temperature and, in the worst case, may result in impossibility of switching operation.